The hypothalamic nuclei, the paraventricular (PVN) and supraoptic (SON) are complex anatomical and biochemical structures. This necessarily limits the interpretation of in vivo studies of neuropeptide secretion. Thus, we have developed a tissue culture model for the study of neurosecretion from microdissected explants of rat PVN and SON. Experiments show that these explants are viable in tissue culture since they 1) secrete vasopressin and oxytocin, 2) adhere to the tissue culture chamber, forming a type of monolayer, 3) incorporate a radioactive amino acid, 35S-cystine, into peptides and proteins, and 4) can be maintained for long periods of time. The most significant advantage of this experimental design is the ability to study localized changes in peptide secretion. We propose to characterize this model for the examination of central neuroendocrine mechanisms. While the focus of the investigation will be the vasopressin-oxytocin axis, the project will extend to the study of other neuropeptides such as corticotropin releasing hormone, atrial natriuretic factor and cholecystokinin. Microdissected PVN and SON nuclear explants from rats will be maintained in tissue culture and characterized by the study of: 1) Neurochemical evaluation of the explants after various times of tissue culture. This will provide information as to the time courses of the changes in neuropeptides, both tissue content and media levels. 2) Histological studies of the explants after various periods of tissue culture. These will include general histological staining, tests for viability and immunocytochemical staining for peptide hormones. 3) Studies of the mechanisms controlling secretion from these hypothalamic regions. The neurosecretory responses to osmotic, hormonal and catecholaminergic stimuli regions will be evaluated as well as tests of specific blocking agents. This new tissue culture model will help to elucidate the complex mechanisms involved in the secretion of paraventricular and supraoptic neuropeptides without the inherent complications of peripheral autonomic, hormonal and osmotic influences.